Modern airlines inventory systems, usually employ complex calculation algorithms for monitoring and managing g up-to-date flights availability. It is more and more usual that a number of independent airlines group together to form an Alliance which could better exploit the different geographical and network capabilities of the single airlines. When such alliances have an interconnected inventory system, the calculation algorithms need to access data from multiple airlines and often from multiple data base systems. According to existing techniques, when the Inventory system of an airline requires inventory data from another airline belonging to the same Airline Alliance, this inventory data are usually accessed in one of the following alternative ways:                remotely, the Inventory system of the other airline being directly accessed in real-time, thanks to dedicated interfaces;        locally, the Inventory system of the other airline regularly pushing its inventory data to the Inventory system of the airline, enabling the latter to replicate required inventory data.        
Both solutions have drawbacks. The first approach requires the Inventory system of the other airline to publish interfaces for accessing inventory data and to be able to cope with the amount of traffic induced. It also makes the Inventory system of the airline dependant on the Inventory system of the other airline, impeding its performances and actually preventing a true real-time usage of the other airline inventory data (network latency to reach the Inventory system of the other airline, processing time of the Inventory system of the other airline to take into account, . . . ).
The second approach requires the Inventory system of the other airline to develop interfaces for exporting inventory data. It also requires the Inventory system of the airline to import the inventory data of the other airline, and completely exclude any possibility of a real-time access to this data.
In both cases, a real-time access to the inventory data of the other airline is actually impossible, implying for instance that availability computed taking into account the other airline inventory data might not be accurate.
Patent application US-A 2002/0147767 discloses a method for monitoring another party's (in this case a competitor's) inventory data by duplicating data on a temporary storage. Such duplication involves the risk that currently accessed data are not up to date with the actual data in the main (original) data base, thus causing possible inconsistency of data, which is not acceptable to the customers.